Process for dehydrating of tar



Dec. 25, 1956 A. KARL PROCESS FOR DEHYDRATING OF TAR Filed Jan. 6, 1954 collector tqnk for flash/I79 t fa ollecfirg main flush/b9 far and emulcion main liguor 5' S 10 ammania dill pressure 6 ref sepa or wheat-erabhydrafed far condensaie ressure reducfion ra/re f 7 1'0 ammonia '6' ill 1D rollecfingmain 1 g flush/kg 3/ 35 E 2.9 pressure u W hr and 7 30 eepmfor gi cal/ecfar tank 32 d h d [Ed for flush/n 28 e y m from gas main j. I; ate!" mam I -/4LFRED KARL JNI/ENTOR.

BY Mam W ATTORNEX PROCESS FOR DEHYDRATING OF TAR Alfred Karl, Essen, Germany Application January 6, 1954, Serial No. 402,456

7 Claims. (Cl. 196-5) The invention is concerned With a method of dehydrating tar, and in particular gas tar, which is separated from the crude gas formed during the dry distillation of coal. In particular the method relates to that kind of dehydration in which hydrated tar is heated under superatmospheric pressure in a container in which the tar and water separate out in superimposed layers and are then withdrawn separately.

The dehydration of tar, and in particular gas tar, is of particular importance to the decomposition of this tar into the fractions which it contains. Modern distillation plants, and particularly those which are continuously operated using so-called flash-evaporation, are sensitive in operation to more than a specific quantity of water in the tar.

Amongst the many prior proposals that have been made for the substantial dehydration of moisture-containing tar before distillation, that which has found most technical use is one which uses heating of the tar under superatmospheric pressure in a closed vessel, this heating under pressure being carried out either continuously or discontinuously and resulting in some of the water separating ofi from the tar, depending on the pressure and temperature employed, so that superimposed layers of water and tar are produced in the pressurised vessel, and these can be withdrawn separately through suitable cocks. This method has been proven useful for a whole series of types of tar whose water content can thereby be reduced to less than It has, however, been found that in the case of certain other kinds of tar it is not possible to bring about sutficient dehydration by this known method. The water content cannot, in these instances, be reduced below 5% and sometimes may even remain considerably above this figure, so that it is then necessary to reboil the tar withdrawn from the pressure vessel to remove further water by evaporation. The boiling of the partiallydehydrated tar, quite apart from the fact that it is troublesome, involves increased expense in the preparation of the tar.

Detailed investigations have now shown that many types of raw tar contain tar-water emulsions which may contain up to 40% of water and which cannot be broken down by normal heating methods under pressure (80 C. and 1-2 atm.) sufiiciently for the water content of the end product to be reduced to less than 5%. These highly aqueous emulsions form an intermediate layer of greater or lesser depth between the water layer and the tar layer in the pressure vessel or pressure separator.

The present invention proposes that this tar-water emulsion be at least partially separately withdrawn and in contrast to the method most employed at the present time and residing in allowing the emulsion to stand for weekly or monthly periods in tar pits--immediately subjected to a special treatment and further quantities of water separated out of the emulsion.

The principle of this invention can be implemented in difierent ways. Thus, for instance, the tar-water emulsion can be subjected to a separate heat treatment under more severe conditions. If, however, this intermediate layer of tar-water emulsion were all to be withdrawn separately and an attempt made to break this whole quantity down, this would occasion a considerable increase in the cost of the complete tar dehydration treatment.

Broadly the instant invention comprises heating the hydrated tar under pressure in an enclosed zone, withdrawing at least part of the tar-water emulsion from the enclosed zone separately from the water and dehydrated tar also in the enclosed zone, subjecting the withdrawn tar-water emulsion to a separate treatment such as expansion for the removal of a portion only of the water therefrom, and returning the non-evaporated component resulting from the expansion or evaporation step to the enclosed zone. If desired, the hydrated tar can be preheated before being passed to the enclosed zone for pressure treatment.

It has now been established that it is only required to draw ofi a fractional amount of this highly aqueous tar emulsion and to submit it to a special treatment, namely more intensive heating under superatmospheric pressure, and then to allow this heated emulsion to expand in an expansion vessel. As a result, a vigorous evaporation of a part of the water contained in the emulsion ensues and the water content of this emulsion is consequently reduced. A further eifect of the expansion is that the steam bubbles developed in the emulsion break the latter up, as a result of which the tar and water form into a mixture which is comparatively simple to split up. The proportion of the thus-treated emulsion which is not evaporated is then delivered back to the pressure separator and decomposed into tar, on the one hand, and water on the other, whilst the steam formed during the expansion is added to the crude gas again.

The proportion of emulsion which is subjected to the special treatment should, in accordance with the invention, represent at the most 25%, and preferably from 10% to 20% of the treated tar product. The heating of the withdrawn portion of the emulsion is, in accordance with a further feature of the invention advantageously carried out at a temperature at the most of 140 C., and preferably to C. Further, the expansion is preferably so operated that the proportion of water which is evaporated during this expansion is at the most 15%, and preferably about 5% to 10%, of the total quantity of water contained in the withdrawn emulsion.

By carrying out the method in the manner indicated, in any event a tar will be obtained with a water content of less than 5% without need for boiling the whole of the tar with a correspondingly large expenditure of heat. In fact it is sufiicient to subject only a comparatively small proportion to a separate heat treatment in order to make the whole of the tar product sufliciently free from water.

Whilst the embodiment of the invention described above is of special advantage in the case of very stubborn emulsions containing a high proportion of water, and even in those instances when the ratio of tar-water emulsion thrown down in the pressure separator is comparatively high relatively to the total quantity of tar, the invention can be differently realised where emulsions which are relatively more easy to break down are concerned, and in this event the separate heat and pressure treatment of the emulsion can be avoided.

Thus, in this further method of carrying the invention into effect the emulsion withdrawn from the pressure separator is returned, without special heat treatment, into the flushing main liquor collector tank from which the hydrated crude tar is forwarded to the pressure separator, being in fact passed directly into the layer of tar at the bottom of this flushing main liquor collector tank without coming into contact with the layer of water located above the tar layer.

The hot tar present in the flushing main liquor collector tank is evidently able to break down considerable quantities of this tar-water emulsion, so that the separation of the water from the emulsion is facilitated. The breaking down of the tar-water emulsion in the tar layer and the flushing main liquor collector tank generally, however, only takes place to an adequate extent when the period during which the tar and the emulsion stay in the flushing main liquor collector tank is so selected that the water content of the tar which is withdrawn from the flushing main liquor collector tank, and after heating is forwarded to the pressure separator, is not more than 25% to 30%.

The dehydration of tar in accordance with this form of the invention may for example be carried out under the following operating conditions:

The tar to be dehydrated is supplied to a flushing main liquor collector tank, which preferably consists of a horizontal cylindrical vessel. The temperature of the tar in the flushing main liquor collector tank is then about 70 C. Advantageously the inflow and outflow to and from the flushing main liquor collector tank is regulated so that about one third of the volume of liquor in the flushing main liquor collector tank is represented by tar and the remaining space is taken up by water or ammoniacal liquor. The rate of flow within the flushing main liquor collector tank is so selected that the period which the tar takes to flow through the collector tank is about twenty-four hours. As a result, the tar is de hydrated until it has a water content of about 25% to 30%, and after withdrawal from the flushing main liquor collector tank is passed to a compression pump which delivers the tar at a pressure of about 2.5 atm. first through a heater, in which the tar is heated to about 85 to 90 C., and subsequently to the tar separator operating under superatmospheric pressure. Tar with a Water content of less than is then withdrawn from the pressure separator. The tar-water emulsion thrown down in the pressure separator is separately withdrawn and re-introduced directly into the flushing main liquor collector tank, preferably in the vicinity of the point of inflow of fresh tar. During the passage of the tar through the flushing main liquor collector tank, a considerable portion of the returned tar-water emulsion is broken down in the hot tar.

The lengthy dwell of the tar in the flushing main liquor collector tank also involves the advantage that an ammoniacal liquor which is practically completely free of tar is produced in this main, and this can be forwarded directly to an ammonia plant.

The methods of this invention can be carried out continuously or discontinuously.

In the accompanying drawings Figure 1 is a diagrammatic flow-sheet of the first-described process herein and Figure 2 is a diagrammatic flow-sheet of the seconddescribed process herein.

In the operation of the invention in accordance with the flow sheet of Figure l, the water-containing gas is passed from the gas main 1 through a line 2 to a collector tank 3 for flushing main liquor. Aqueous condensate from the coal gas is removed from the upper portion of this collector tank 3 through an outlet line 4 and passed to the collecting main to flush the main and cool the gases therein. Water-containing tar is removed from the lower portion of the collector tank 3 for flushing main liquor and passed through an outlet line 5 to a pump 6 which delivers this tar under superatmospheric pressure to a tar separator 7 which operates under superatmospheric pressure. The water-containing tar is heated under pressure in this separator 7. As a result, dehydrated tar passes to the bottom of the separator where it is withdrawn through an outlet line 8. An aqueous layer forms in the upper portion of the pressure separator 7 and a layer of tar water emulsion forms intermediate the dehydrated tar and aqueous layers. The aqueous layer is removed from the upper portion of the pressure separator 7 through an outlet line 9 and passed to a still for recovery of the ammonia. A portion of the tar-water emulsion is removed from the pressure separator 7 through an outlet line 8 and passed to a heater 11 provided with heating media inlet and outlet lines 12 and 13 respectively and operating under superatmospheric pressure where the emulsion is subjected to intensive heating under superatmospheric pressure. The heated emulsion is then passed through a valved line 14 to an expansion vessel 15' where a minor part of the water present in the emulsion is removed from this emulsion as steam. The steam is returned to the gas main 1 through a steam line 16. and the proportion of the partially dehydrated emulsion is passed through a valved outlet line 17 to a storage container 18. A portion of the treated emulsion can be withdrawn from this valved outlet line 17 connecting the expansion vessel 15 and the storage vessel 18 through a valved line 19 and passed by means of a pump 20 through a line 21 to the gas main. The partially dehydrated emulsion is then passed by means of a line 22 to the collector tank 3 for flushing main liquor where it comes into contact with water-containing tar from the collecting main 23. The treated emulsion along with the water-containing tar from the gas main 1 is then passed through a line 5 to the pump 6 which delivers this treated emulsion and water-containing tar back to the pressure separator 7 wherein the treated emulsion is decomposed or separated collector tank 26 through an outlet line 28 and passed to a pump 29 which delivers this tar under pressure, first through a heater 30 provided with heating medium inlet and outlet lines 31 and 32 respectively, and then to a separating chamber 33 which operates under superatmospheric pressure. this pressure separator 33 where it is withdrawn through an outlet line 34. An aqueous layer forms in the upper portion of the pressure separator 33 and a layer'of tar- Water emulsion forms intermediate the dehydrated tar and aqueous layers. The aqueous layer is removed from the upper portion of the pressure separator 33 through an outlet line 35 and passed to a still (not shown) for recovery of ammonia. tar-Water emulsion is removed from the pressure separator 33 and passed through a valved line 36 which is also equipped with a pressure reduction valve 37 which lowers the pressure on the emulsion, and this emulsion is then passed directly into the water-containing tar layer in the lower portion of the collector tank 26 in the vicinity or region of the newly-incoming hot, water-containing tar without contacting the water layer located above this tar layer. The hot tar present in the collector tank 26 evidently breaks down a considerable portionof the'tarwater emulsion and a part of the water is evaporated from the emulsion and returned to the collecting main (not shown) through an outlet line 27 to flush the main and cool the gases therein. The partially broken emulsion is then Withdrawn from the bottom portion of the collector tank 26 through an outlet line 28 and passed by means of the pump 29 first through heater 30 and then to the pressure separator 33 wherein this partially broken i emulsion is completely decomposed or separated into dehydrated tar and water.

I claim:

l. A method of dehydrating water-containing tar derived from a tar-containing crude gas formed during the dry distillation of coal which comprises heating said Water-containing tar under superatmospheric pressure in Dehydrated tar passes to the bottom of A At least a minor portion of the an enclosed separator zone to cause the formation therein of superimposed layers of dehydrated tar, tar-Water emulsion and water; withdrawing a minor portion of said tarwater emulsion from said enclosed zone separately from said layer of water and said layer of dehydrated tar also present therein; heating such withdrawn emulsion in an enclosed zone to a temperature exceeding that in the enclosed separator zone; passing said heated emulsion to an expansion zone maintained at a pressure below that obtaining within said enclosed zone thereby to cause vigorous ebullition of the Water content of the emulsion and evaporation of a portion of such water content, and returning the non-evaporated component to said enclosed separator zone.

2. The method of claim 1 wherein the vapors produced in said expansion zone are passed to the tarcontaining crude gas.

3. The method of claim 1, in which the tar-water emulsion is withdrawn in an amount not exceeding 25% of the treated tar.

4. The method of claim 1, in which the expansion step is controlled to evaporate not more than 15% of the water in the withdrawn portion of tar-water emulsion.

5. The method of claim 1, in which the withdrawn portion of tar-water emulsion is heated to a temperature not exceeding 140 C.

6. A method of dehydrating water-containing tar derived from a tar-containing crude gas formed during the dry distillation of coal, which comprises allowing watercontaining tar to stand under normal pressure in a preliminary settling zone for preliminary separation into a water layer and a water-containing tar layer, withdrawing tar from the water-containing, tar layer in said settling zone and passing this tar to an enclosed separator zone, heating said water-containing tar in said enclosed separator zone under superatmospheric pressure to cause the formation therein of superimposed layers of dehydrated tar, tar-water emulsion and water; withdrawing at least a minor portion of said tar-water emulsion from said separator zone separately from said layer of water and said layer of dehydrated tar also present therein, and thereafter returning withdrawn emulsion under less pressure than in said separator zone directly into the layer of water-containing tar present in the lower part of said preliminary settling zone in the region of the point of inflow of newly-incoming hot, water-containing tar thereto While avoiding contact between said tar-water emulsion and the water layer located above said layer of water-containing tar, the period during which said emulsion is allowed to stay in said preliminary settling zone being so selected that the water content of the tar which is subsequently withdrawn from said preliminary settling zone and forwarded, after heating, to said enclosed separator zone does not exceed 30%.

7. A method of dehydrating water-containing tar which comprises heating said water-containing tar under superatmospheric pressure in an enclosed separator zone to cause the formation therein of superimposed layers of dehydrated tar, tar-water emulsion and water; withdrawing at least a portion of said tar-Water emulsion from said enclosed zone separately from the water layer and the dehydrated tar layer also present therein, expanding said withdrawn tar-water emulsion to evaporate a portion of the water therefrom, and returning the non-evaporated component to said enclosed separator zone.

References Cited in the file of this patent UNITED STATES PATENTS 1,660,235 Peirce Feb. 21, 1928 1,847,654 Kleinman Mar. 1, 1932 1,958,583 Miller May 15, 1934 2,366,899 Hall et al. Jan. 9, 1945 2,383,362 Batchelder Aug. 21, 1945 FOREIGN PATENTS 680,244 Great Britain Oct. 1, 1952 

1. A METHOD OF DEHYDRATING WATER-CONTAINING TAR DERIVED FROM A TAR-CONTAINING CRUDE GAS FORMED DURING THE DRY DISTILLATION OF COAL WHICH COMPRISES HEATING SAID WATER-CONTAINING TAR UNDER SUPERATMOSPHERIC PRESSURE IN AN ENCLOSED SEPARATOR ZONE TO CAUSE THE FORMATION THEREIN OF SUPERIMPOSED LAYERS OF DEHYDRATED TAR, TAR-WATER EMULSION AND WATER; WITHDRAWING A MINOR PORTION OF SAID TARWATER EMULSION FROM SAID ENCLOSED ZONE SEPARATELY FROM SAID LAYER OF WATER AND SAID LAYER OF DEHYDRATED TAR ALSO 